Rotary piercing processes



7 y 1957 L. E. SAWYER 2,791,924

ROTARY PIERCING PROCESSES Filed Aug. 25, 1951 FIG. \2A

FIG. 2C

INVENTOR BY L ukeESah yez ATTORNEY ROTARY PIERCING PROCESSES Luke E. Sawyer, Chippewa Township, Pa., assignor, by mesne assignments, to The Bahcock 65 Wilcox Cornpany, Jersey City, N. J., a corporation of New .iersey Application August 25, 1951, Serial No. 243,727

2 Claims. (Cl. 80-62) The present invention relates to improvements in rotary piercing processes and the like and more particularly, to the rotary piercing of hot billets of austenitic stainless steel alloys and other metals and metal alloys diflicult to pierce, in the manufacture of seamless hollows or tubes.

All commercial rotary piercing processes have the common feature of the formation of a hollow by peripherally rolling a hot cylindrical billet over a conical mandrel by driven rolls set at an angle to the horizontal plane through the center line of the piercing mill. The action of the piercer rolls or cones consists of gripping the hot billet, advancing it by reason of the skew rolling action imparted by the feed angle of the roll axes, reducing the diameter of the billet, and then helically rolling the reduced billet over the conical mandrel between the driven rolls and offset guide rolls.

The rotary piercing of high alloy steels of the stainless type, even when the alloy constituents have been balanced in an effort to stabilize the phase of the alloy and effect improvement in high temperature ductility, has proved to be much more difficult than piercing billets of carbon steels. A suitable metal ductility when hot is necessary to withstand the various tensional, compressional, and torsional forces set up in piercing. The deformation of the metal in rotary piercing involves peripheral skew rolling which is largely compressive in nature, a reduction in wall thickness, a bending action on the outermost and innermost surfaces of the hollow, an abrading action on the inner and outer surfaces of the hollow caused by differences in the relative surface speeds of the hollow, mandrel and the driven and guide rolls, and a twisting action caused by the differential peripheral speeds of the hollow and the rolls at various points in the pass. A high degree of care must be exercised in such cases to provide the proper roll feed angle, suitable speeds of the piercer rolls, and a careful location of the piercing point to minimize internal marking of the pierced hollow. To secure the proper relative positions of the piercing point and billet, it is now customary to provide by drilling, burning or punching a center recess or starting hole in the billet end in which 4 the piercing point is centered at the start of the piercing operation.

Even when the piercing point is made of a metal or metal alloy which has the desiredqualities of toughness and wear resistance at high temperatures, and which does not spall or crack at the surface when the working layer is heated to a high temperature while the body remains at a much lower temperature, it has been found with billets of the character described, that the internal surface of the pierced hollow has been marked or fissured to an extent requiring a further conditioning operation to secure the nite ates Patent F ice desired inside finish before repiercing or drawing the pierced hollow. Efforts have heretofore been made to lubricate the piercing point to lengthen the working life of the point, and also to improve the internal surface condition of the hollow. The most common means of point lubrication is to form a smooth scale on the piercing point. This is done by heating the -points in an annealing furnace and then breaking them in by first using them on billets of carbon steel. This breaking-in process provides a surface scale which acts to lubricate the point during its subsequent use in stainless steel billet piercing.

In accordance with the present invention I provide a special solid incombustible lubricant for the piercing point for the rotary piercing of billets of the character described, which results in a substantial saving in the labor required for conditioning the internal surface of the pierced hollows, and which also, results in savings in grinding loss, crop less, power consumption, and wear on the piercing points and conditioning tools. This involves the provision of a glass-like lubricant having a relatively widefusion temperature range at and below the billet hot working temperature over which it becomes progres sively more mobile as its temperature increases, while still retaining some viscosity, during the entire piercing operation. Ordinary bottle glass has proved to be a satisfactory material for this purpose and the lubricant material may be in the form of a bottle bottom section, fiber glass, and/or granulated glass.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred form of my invention.

Of the drawings:

Fig. 1 is a diagrammatic illustration of a cone-type piercing mill, to the operation of which the invention is applicable;

Fig. 2 is an enlarged view of the roll pass shown in Fig. 1;

Figs. 2A to 2H are sections taken on the lines A to H respectively illustrating different stages through the roll pass;

Fig. 3 is a vertical section through a billet end with the glass lubricating material inposition; and

Fig. 4 is an end view of the billet shown in Fig. 3.

While the present invention is also adapted for use in other commercial types of piercing mills, such as the Mannesmann or parallel axis barrel type roll piercing mill or the Stiefel or degree disc mill, it has been illustrated as applied to a 60 degree cone roll piercing mill in which a solid billet iii is rotated and advanced by a pair of angularly arranged diametrically opposite piercer rolls 12 rotated in the directions indicated by the arrows in Fig. 1 to cause the rotating billet to flow over and about a conical piercing point 14 mounted'on a bar 16. The piercing point is held against longitudinal movement but is free to rotate with the billet being pierced.

Figures 2A to 2H show a series of sections through a typical hollow as made on a 60 degree cone-type piercing mill. As shown by the successive sections, the hollow passes through an oval or slightly rectangular section near the center of the pass, and is rounded up by the action of the piercer rolls at the outlet of the pass. At this point Patented May 14, 1957.

the external and internal periphery of the hollow is established and the rounding action separates the hollow from the piercing point so that it can be readily stripped from the piercer bar and passed along to the next operation.

In accordance with the invention the workpieces to be pierced are usually in the form of cylindrical billets and are first provided with a circular center recess 20 concentrio with the billet axis which may correspond to the customary centering recess or starting hole provided for centering the piercing point or may be specially formed for the purposes of this invention. In either case the recess is made deep enough to receive and hold the desired amount of lubricating material while the billet is in a horizontal position. For example, I have used an end hole 1%" in diameter X 1 /2 deep for a cylindrical billet 3 in diameter.

The billets so formed are heated in a suitable billet heating furnace to the desired hot working temperature, and when discharged from the furnace are successively pushed into the piercing mill. In accordance with the invention a body or mass of solid incombustible material, which is fusible when in contact with a billet at its piercing temperature, and which has a relatively wide range of fusion temperatures at and below the billet hot working temperature throughout which it remains in a condition of varying viscosity, is inserted in the recess a short time, e. g. 5-15 seconds, prior to the heated billet entering the piercer rolls. I have found that ordinary bottle glass will provide an excellent lubricant for such work under these conditions. The glass lubricant is preferably in the form of the bottom section 22 of a substantially cylindrical glass bottle filled with a mass of ordinary fiber glass 24, to insure a symmetrical distribution of the lubricant relative to the piercing point even when the point is in its customary horizontal position, and even if the bottle section itself should crack or shatter due to temperature shock on its insertion. .The bottle section preferably has a depth slightly less than the depth of the recess 20, and of a diameter adapted to snugly fit into the recess, so that it is not likely to fall out of the recess when the billet is in a horizontal position. The relatively short time interval between insertion of the lubricant and entry of the piercing point into the center recess is ordinarily sufiicient to bring at least the surface of the bottle section in contact with the billet to a fused viscous condition before the entrance of the piercing point. The remaining portion of the body of glass is compressed between the working surface of the piercing point and billet and continues to fuse during the piercing operation, so that at all times the working section of the piercing point is separated from the billet internal surface by a relatively thin layer of glass having a fused outer layer in contact with the working surfaces of the billet and a continuously thinning inner layer of relatively solid glass. The amount of glass lubricant employed is made suflicient to provide the described lubrication throughout the length of the billet being pierced. The heating effect of the hot billet and the heat generated by friction during the piercing operation insure that the outer layer of lubricant will be maintained in a fused viscous condition.

The use of a glass lubricant in the manner describe has been found to result in a substantial improvement in the condition of the internal surface of the pierced hollow and to substantially reduce, if not completely eliminate, the labor required for subsequently conditioning this surface, as well as resulting in savings in grinding loss, crop loss, power consumption, and wear on the piercing points and the tools used in grinding. In a series of tests in which 813 pieces of stainless steel alloys (27% chromium and 18% chrome-8% nickel alone and with various additions of columbium or titanium) were rotary pierced as described, 434 using a glass lubricant and 379 without any lubricant, the following savings in man hours for conditioning the internal surface of the pierced hollows were found:

Semi-finished tubes I. D. Good. Time Hrs. Per Hollow Pos. Test No. Billet Billet Wall Savlng Material Size Thickness With- With out Glass Glass l8- 8 4 x 52.5 320 17. G 4 8. 2 l8Ei-Cb 4 X 52.5 320 19. 1 12.4 6. 7 l8-8 Tl 4 X 52.5 .1520 20.9 10.6 10.3 lS-Si-Cb 4 x 52.5 .320 19.2 13.0 6.2

Average 19.2 11.35 7.85

40.9% savings in man hours.

Finished tubes I D. Gond Time hrs. per Billet Hollow 100 P05 Test No. Mate- Billet Size Wall Savrial Thickings ness Wlth- W h out Glass Glass 4 X 46 .320 131.3 60. 9 64.4 4.5 x 58 320 206. 9 157. 2 49. 7 4.5 x 61.5 .250 23. 5 0.0 23. 'i 5 Y 7L5 535 100. '3 52. 1. 43. 2 5" r 79 .638 157.2 18.7 138. 5

Average 123. 84 58. 98 G4. 86

52.4% savings in man hours.

The labor now required for conditioning the internal changes may be made in the process disclosed without departing from the spirit of the invention covered by my claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features, as, for example, in processes of re-piercing, plug rolling or elongating in which a hollow is hot worked over a mandrel. With certain types of billet heating furnaces, the glass lubricant may advantageously be inserted in the end recess prior to the billet heating operation.

I claim:

1. The method of rotary piercing a hot metal workpiece of circular cross-section having a center opening of substantial depth in one end thereof which comprises heating the billet to its hot working temperature, placing in the center opening a body of self-sustaining incombustible lubricating material having a relatively wide range of fusion temperatures below the workpiece hot working temperature, rotating and axially advancing the workpiece While at a predetermined hot working temperature by a skew roiling action relative to a conical piercing point with the point horizontally aligned with the center opening and the lubricating material symmetrically arranged in the center opening relative to the piercing point, and, before the heat of the workpiece objectionably fuses the body of lubricating material, piercing the workpiece at such a rate that the lubricating material contacting with the hot workpiece progressively fuses and forms an outer layer of fused lubricating material and a continuously thinning inner layer of relatively solid lubricating material between the working surface of the piercing point and the portions of the workpiece contacting therewith.

References Cited in the file of this patent UNITED STATES PATENTS Mannesmann Apr. 26, 1887 Nelson Aug. 23, 1930 Bark Feb. 6, 1934 Novack July 25, 1939 Orozco May 10, 1949 Sejournet Jan. 23, 1951 Sejournet Mar. 3, 1953 Sejournet Apr. 26, 1955 FOREIGN PATENTS Great Britain Mar. 12, 1948 

